CN111352124A - Doppler signal demodulation method and system thereof - Google Patents
Doppler signal demodulation method and system thereof Download PDFInfo
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- CN111352124A CN111352124A CN201811570315.4A CN201811570315A CN111352124A CN 111352124 A CN111352124 A CN 111352124A CN 201811570315 A CN201811570315 A CN 201811570315A CN 111352124 A CN111352124 A CN 111352124A
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
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- G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
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Abstract
A Doppler signal demodulation method and system. The Doppler signal demodulation method comprises the following steps: amplifying the obtained Doppler signals to obtain amplified Doppler signals, wherein the Doppler signals are detected Doppler frequency shifts caused by the movement of the measured object; performing band-pass filtering processing on the amplified Doppler signal to obtain a filtered Doppler signal as an input signal for filtering additive noise in the input signal; and performing phase-locked demodulation on the input signal by using a phase-locked loop demodulation module to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so as to calculate the movement speed of the object to be measured through the demodulated signal.
Description
Technical Field
The invention relates to the technical field of laser vibration measurement, in particular to a Doppler signal demodulation method and a Doppler signal demodulation system.
Background
Basic principle of laser doppler technique: the velocity of the movement of the object to be measured is detected by detecting the doppler shift caused by the movement of the object to be measured. The doppler shift is demodulated to obtain the moving speed of the object to be measured. In a conventional digital demodulation mode, a high-speed ADC (analog-to-digital converter) is generally used to acquire a two-way heterodyne laser signal, and according to a relationship between an optical path difference and a phase difference, an FPGA (field programmable gate array) digital processing mode is used to obtain a digital displacement amount, and then the digital displacement amount is converted into an analog voltage through a DAC (digital-to-analog converter) with high resolution and output the analog voltage.
However, the digital demodulation method not only requires high price of the required devices and complex signal processing algorithm, but also is easily interfered by the external environment, and has high requirement on the signal-to-noise ratio of the measurement signal, so that the demodulation is easily interfered by the external environment, and cannot be adapted to precise measurement in a severe environment. Therefore, in order to solve the above problems, a new doppler signal demodulation method or demodulation system is urgently needed.
Disclosure of Invention
The invention provides a Doppler signal demodulation method and a system thereof, which can filter out a plurality of phase noises in an input signal and compress bandwidth, so that the carrier-to-noise ratio of the input signal is very low, and a demodulated output signal is very pure, thereby being particularly suitable for precision measurement in severe environment. Of course, the laser external reference Doppler signal demodulation method and the system thereof can also effectively reduce the frequency modulation receiving threshold and improve the receiving sensitivity.
In addition, the laser external reference Doppler signal demodulation method and the system thereof solve the problem of speed decoding of the laser external reference Doppler signal, can be suitable for laser Doppler speed demodulation in a low signal-to-noise ratio environment, can also be suitable for signal demodulation (such as demodulation of a laser heterodyne interference signal) of a laser vibration measurement (velocity measurement) instrument, and are a laser external reference Doppler signal demodulation circuit with high cost performance and high precision.
To achieve at least one of the above objects or other objects and advantages, the present invention provides a doppler signal demodulation method including the steps of:
amplifying the obtained Doppler signals to obtain amplified Doppler signals, wherein the Doppler signals are detected Doppler frequency shifts caused by the movement of the measured object;
performing band-pass filtering processing on the amplified Doppler signal to obtain a filtered Doppler signal as an input signal, wherein the filtered Doppler signal is used for filtering additional noise in the input signal; and
and performing phase-locked demodulation on the input signal by using a phase-locked loop demodulation module to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated by the demodulated signal.
In an embodiment of the present invention, the step of performing phase-locked demodulation on the input signal by using a phase-locked loop demodulation module to output a speed demodulation signal as an output signal includes the steps of:
comparing, by a phase comparator of the pll demodulation module, a phase difference between the input signal and a comparison signal output by a voltage controlled oscillator of the pll demodulation module to obtain an error voltage;
filtering a modulation carrier component in the error voltage by a loop filter of the phase-locked loop demodulation module to obtain a control voltage;
adjusting the frequency of the comparison signal output by the voltage-controlled oscillator by the control voltage so that the comparison signal has a predetermined frequency relationship with the input signal; and
and outputting the control voltage as the demodulation signal.
In an embodiment of the invention, the frequency of the comparison signal is equal to the frequency of the input signal.
In an embodiment of the invention, a ratio between a frequency of the comparison signal and a frequency of the input signal is kept constant.
In an embodiment of the invention, a difference between the frequency of the comparison signal and the frequency of the input signal remains unchanged.
In an embodiment of the present invention, between the amplifying processing step and the filtering processing step, the method further includes the steps of:
and performing frequency mixing processing on the amplified Doppler signals to obtain frequency-mixed Doppler signals, wherein the center frequency of the frequency-mixed Doppler signals is matched with the working frequency of the phase-locked loop demodulation module.
In an embodiment of the present invention, between the filtering processing step and the phase-locked demodulation step, the method further includes the steps of:
and carrying out amplitude limiting processing on the input signal so as to enable the amplitude of the input signal to be matched with the working amplitude of the phase-locked loop demodulation module.
In an embodiment of the present invention, after the phase-locked demodulation step, the method further includes the steps of:
amplifying the demodulation signal to obtain an amplified demodulation signal; and
and performing active filtering processing on the amplified demodulation signal to filter noise in the amplified demodulation signal.
According to another aspect of the present invention, there is also provided a doppler signal demodulation system including:
the pre-stage amplification module is used for amplifying the obtained Doppler signal to obtain an amplified Doppler signal, wherein the Doppler signal is a detected Doppler frequency shift caused by the movement of a measured object;
a band-pass filtering module, configured to perform band-pass filtering processing on the amplified doppler signal to obtain a filtered doppler signal as an input signal, so as to filter additional noise in the input signal; and the phase-locked loop demodulation module is used for performing phase-locked demodulation on the input signal to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated through the demodulated signal.
In an embodiment of the present invention, the pll demodulation module includes a phase comparator, a loop filter, and a voltage-controlled oscillator communicably connected to each other, wherein the phase comparator is configured to compare a phase difference between the input signal and a comparison signal output by a voltage-controlled oscillator of the pll demodulation module to obtain an error voltage; the loop filter is used for filtering a modulation carrier component in the error voltage to obtain a control voltage; the voltage-controlled oscillator is used for adjusting the frequency of the comparison signal output by the voltage-controlled oscillator through the control voltage so that the comparison signal and the input signal have a preset frequency relation; and the loop filter is further configured to output the control voltage as the demodulation signal.
In an embodiment of the present invention, the doppler signal demodulation system further includes a frequency mixing module, configured to perform frequency mixing processing on the amplified doppler signal to obtain a frequency-mixed doppler signal, where a center frequency of the frequency-mixed doppler signal matches with a working frequency of the phase-locked loop demodulation module.
In an embodiment of the present invention, the doppler signal demodulation system further includes a limiting module, configured to perform limiting processing on the input signal, so that an amplitude of the input signal matches an operating amplitude of the phase-locked loop demodulation module.
In an embodiment of the present invention, the doppler signal demodulation system further includes a post-amplification module and an active filtering module, wherein the post-amplification module is configured to amplify the demodulated signal to obtain an amplified demodulated signal; the active filtering module is used for performing active filtering processing on the amplified demodulation signal so as to filter noise in the amplified demodulation signal.
In an embodiment of the invention, the pll demodulation module is a pll demodulation circuit.
In an embodiment of the invention, the pre-amplification module is a wideband pre-op amp circuit.
In an embodiment of the invention, the band-pass filtering module is a band-pass filter or an intermediate frequency filter.
Further objects and advantages of the invention will be fully apparent from the ensuing description and drawings.
These and other objects, features and advantages of the present invention will become more fully apparent from the following detailed description, the accompanying drawings and the claims.
Drawings
Fig. 1 is a flowchart illustrating a doppler signal demodulation method according to an embodiment of the invention.
Fig. 2 is a flow chart illustrating one of the steps of the doppler signal demodulation method according to the above-described embodiment of the present invention.
Fig. 3 shows an example of a schematic block diagram of a phase locked loop demodulation module according to the invention.
Fig. 4 shows a simplified schematic diagram of a phase-locked loop demodulation module according to the present invention.
Fig. 5 shows a detailed schematic diagram of a phase locked loop demodulation module according to the present invention.
Fig. 6 is a block diagram schematically illustrating the doppler signal demodulation system according to the above-described embodiment of the present invention.
Fig. 7 is a flowchart illustrating a method for demodulating a doppler signal according to an embodiment of the present invention.
Fig. 8 is a block diagram schematically illustrating the doppler signal demodulation system according to the above-described embodiment of the present invention.
Detailed Description
The following description is presented to disclose the invention so as to enable any person skilled in the art to practice the invention. The preferred embodiments in the following description are given by way of example only, and other obvious variations will occur to those skilled in the art. The basic principles of the invention, as defined in the following description, may be applied to other embodiments, variations, modifications, equivalents, and other technical solutions without departing from the spirit and scope of the invention.
In the present invention, the terms "a" and "an" in the claims and the description should be understood as meaning "one or more", that is, one element may be one in number in one embodiment, and the element may be more than one in number in another embodiment. The terms "a" and "an" should not be construed as limiting the number unless the number of such elements is explicitly recited as one in the present disclosure, but rather the terms "a" and "an" should not be construed as being limited to only one of the number.
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless explicitly stated or limited otherwise, the terms "connected" and "connected" are to be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
With the rapid development of laser technology, the technology for measuring the vibration amplitude, speed and acceleration and the mechanical shock speed and acceleration by using the laser technology (i.e. laser vibration measurement technology, also called laser speed measurement technology or laser doppler technology) is also rapidly developed. In addition, the laser vibration measurement technology is closely related to the production and life of human beings, is widely applied to the aspects of material flaw detection, fault diagnosis of a mechanical system, noise elimination, dynamic characteristic analysis of a structural member, verification of a finite element calculation result of vibration and the like, and can promote the production and life quality of human beings to develop towards a better and more complete direction.
However, the doppler signal demodulation technique is an important guarantee for accurately obtaining the movement velocity or vibration amplitude of the object to be measured as a critical part of the laser vibration measurement technique. The conventional doppler signal demodulation technology generally uses a digital demodulation mode to acquire a two-way heterodyne laser signal through a high-speed ADC (analog-to-digital converter), obtains a digital displacement by an FPGA (field programmable gate array) digital processing mode according to a relationship between an optical path difference and a phase difference, and converts the digital displacement into an analog voltage through a high-resolution DAC (digital-to-analog converter) for output. However, in the digital demodulation mode, not only are the required devices expensive and the signal processing algorithm complex, but also the demodulation is easily interfered by the external environment, and the requirement on the signal-to-noise ratio of the measurement signal is high, so that the demodulation is easily interfered by the external environment, and the digital demodulation mode cannot be adapted to the precise measurement in the severe environment. Therefore, in order to solve the above problems, a new doppler signal demodulation method or a doppler signal demodulation system is urgently needed.
Referring to fig. 1 to 6 of the drawings, a doppler signal demodulation method and a system thereof according to an embodiment of the present invention are illustrated. Specifically, as shown in fig. 1, the doppler signal demodulation method includes the steps of:
s110: amplifying the obtained Doppler signals to obtain amplified Doppler signals, wherein the Doppler signals are detected Doppler frequency shifts caused by the movement of the measured object;
s120: performing band-pass filtering processing on the amplified Doppler signal to obtain a filtered Doppler signal as an input signal, so that additional noise in the input signal is eliminated; and
s130: and performing phase-locked demodulation on the input signal by using a phase-locked loop demodulation module to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated by the demodulated signal.
In this embodiment of the present invention, for example, since the doppler shift (i.e., doppler signal) caused by the movement of the measured object detected by the laser vibration measurement (velocity measurement) instrument is generally weak, the obtained doppler signal needs to be amplified first so that the doppler signal is amplified to a certain extent to obtain the amplified doppler signal; then, performing band-pass filtering processing on the amplified Doppler signal to eliminate additional noise in the amplified Doppler signal, and using the filtered Doppler signal as an input signal of the phase-locked loop demodulation module; and finally, the phase-locked loop demodulation module performs phase-locked demodulation on the input signal to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated through the demodulated signal. In other words, the phase-locked loop demodulation module is used for converting the frequency conversion of the input signal into the voltage variation of the demodulation signal, so that after the demodulation signal is obtained, the Doppler velocity measurement formula can be used
And calculating the motion speed value of the measured object. It is understood that the doppler signal obtained by a laser vibration measuring (velocimetry) instrument is the doppler shift between scattered light and incident light.
It should be noted that, in this embodiment of the present invention, the doppler signal demodulation method demodulates the doppler signal by an analog signal processing manner, without performing conversion between an analog signal and a digital signal, and without performing complicated calculation by a digital algorithm. Therefore, the Doppler signal demodulation method not only can avoid using expensive devices and complex signal processing algorithms, but also can reduce the interference of the external environment, and can effectively reduce the frequency modulation receiving threshold and improve the receiving sensitivity. In other words, the doppler signal demodulation method can filter out phase noise in the input signal, compress the bandwidth, make the input carrier-to-noise ratio very low, and the demodulation signal obtained by demodulation processing is very pure, and is particularly suitable for precision measurement in severe environment.
It should be noted that, in this embodiment of the present invention, the PLL demodulation module may be implemented as, but not limited to, a PLL demodulation circuit, where phase locking means automatic control of phase synchronization, and an automatic control closed-loop system capable of performing phase synchronization of two electrical signals is called a PLL, for short. The method is widely applied to the technical fields of broadcast communication, frequency synthesis, automatic control, clock synchronization and the like, and is used for obtaining a comparison signal output by a voltage controlled oscillator (VCO for short). In the embodiment of the present invention, the demodulation signal output by the pll demodulation module is a control voltage input to the vco.
Specifically, as shown in fig. 2, the step S130 includes the steps of:
s131: comparing, by a phase comparator of the pll demodulation module, a phase difference between the input signal and a comparison signal output by a voltage controlled oscillator of the pll demodulation module to obtain an error voltage;
s132: filtering a modulation carrier component in the error voltage by a loop filter of the phase-locked loop demodulation module to obtain a control voltage;
s133: outputting, by the voltage-controlled oscillator, a comparison signal of a corresponding frequency based on the control voltage so that the frequency of the comparison signal is equal to the frequency of the input signal; and
s134: and outputting the control voltage as the demodulation signal.
Illustratively, as shown in fig. 3, the pll demodulation circuit generally includes three parts, i.e., a phase comparator (PC for short), a voltage-controlled oscillator (vco) outputting a comparison signal U, and a loop filter0Connected to an input of the phase comparator, the loop filters being connected to an output of the phase comparator and to an input of the voltage-controlled oscillator, respectively. The pressure controlSaid comparison signal U of the oscillator0Frequency f of2Is controlled by a control voltage U established on the loop filterdIs determined. When inputting signal UiIs applied to the other input of the phase comparator, the input signal U is first compared by the phase comparatoriAnd the comparison signal U0To generate an error voltage UψWherein the error voltage UψIs proportional to the input signal UiAnd the comparison signal U0A phase difference therebetween; then, the error voltage U is filtered by the loop filterψAfter medium high frequency component, the control voltage U is obtaineddTo pass through the control voltage UdTo adjust the comparison signal U of the voltage controlled oscillator0Frequency f of2High and low. Due to the control voltage UdTowards reducing the input signal UiFrequency f of1With said comparison signal U0Frequency f of2The direction of the difference changes until the comparison signal U0Frequency f of2And the input signal UiFrequency f of1Are kept equal when the comparison signal U is present0And the input signal UiIs called phase lock because it remains constant (i.e., synchronous). At this time, the control voltage U is outputdAnd the motion speed value of the object to be measured is calculated by the control voltage as a demodulation signal of the phase-locked loop demodulation circuit.
In other words, when a frequency modulated signal (i.e., an input signal) is input to the phase locked loop circuit, the voltage controlled oscillator tracks the frequency variation of the input signal. When the input frequency is high, the output of the phase comparator is shifted to the positive side and changed, and the loop filter controls the voltage-controlled oscillator to change the oscillation frequency of the voltage-controlled oscillator; when the frequency of the input signal becomes low, the oscillation frequency of the voltage-controlled oscillator shifts to the negative side and changes down, and the frequency change of the input signal is tracked. Then from the change in the control voltage output by the loop filter, it can be seen that its frequency changes proportionally. Therefore, the frequency variation of the input signal is converted into the voltage high-low variation, so that the phase-locked loop demodulation circuit forms a loop of voltage-frequency conversion, and forms a demodulation circuit of a Doppler signal (namely Doppler frequency shift).
Of course, in other examples of the present invention, the frequency of the comparison signal generated by the voltage-controlled oscillator may not be equal to the frequency of the input signal, but the comparison signal and the input signal are required to maintain a predetermined frequency relationship to meet different operation requirements, for example, the ratio of the frequency of the comparison signal to the frequency of the input signal is kept unchanged; or the difference between the frequency of the comparison signal and the frequency of the input signal remains unchanged.
It is noted that the pll demodulation circuit also has the capability of "catching" the signal when the pll demodulation circuit is locked, i.e. the pll demodulation circuit can automatically track the input signal variation within a certain range, and if the input signal frequency varies within the catching range of the pll demodulation circuit, the pll demodulation circuit can catch the input signal frequency and force the pll demodulation circuit to lock on this frequency. Further reference may be made to U.S. patent application publication No. US20110025386a1 entitled "Phase-Locked Loop" for more details regarding Phase-Locked loops.
Illustratively, as shown in fig. 4, the pll demodulation circuit may be, but is not limited to, implemented as a CD4046 pll, when the frequency-modulated signal is amplified, filtered and ac-coupled as an input signal to the input terminal 14 of the CD4046 pll, the center frequency of the CD4046 pll is equal to the frequency of the frequency-modulated signal, which causes a different phase difference between the comparison signal output by the vco and the input signal, so as to generate a voltage variation corresponding to the frequency variation of the input signal at the input terminal of the vco, and the voltage variation is isolated by the source follower and then outputs a demodulated signal at the demodulation output terminal 10 of the CD4046 pll.
In more detail, as shown in fig. 5, the working principle of the CD4046 phase-locked loop is as follows: input signal UiAfter the input is carried out from a pin 14, the input is amplified and shaped by an amplifier A1 and then is added to the input ends of phase comparators I and II; when the switch K is switched to the 2 pin, the comparator I compares the phase of the comparison signal input from the 3 pin with the phase of the input signal, and the error voltage output from the phase comparator reflects the phase difference of the two signals; filtering with R3, R4 and C2 to obtain a control voltage UdThe voltage control oscillator is added to an input end 9 pin of a Voltage Controlled Oscillator (VCO) to adjust the oscillation frequency of the VCO so that the oscillation frequency approaches to the signal frequency quickly; the comparison signal output by the voltage-controlled oscillator enters the phase comparator I again through the divider, phase comparison is continuously carried out on the comparison signal and the input signal, finally the frequency of the comparison signal is equal to the frequency of the input signal, the phase difference between the comparison signal and the input signal is a certain value, phase locking is achieved, and the control voltage input into the voltage-controlled oscillator is output as a demodulation signal. If the switch K is turned to the pin 13, the phase comparator II works, and the working process of the phase comparator II is the same as that of the phase comparator I.
According to the above embodiment of the present invention, as shown in fig. 1, the doppler signal demodulation method further includes the steps of:
s140: amplifying the demodulation signal to obtain an amplified demodulation signal; and
s150: and performing active filtering processing on the amplified demodulation signal to filter noise in the amplified demodulation signal, so as to output a demodulation signal with a pure frequency spectrum.
It should be noted that the signal strength of the demodulated signal output by the phase-locked loop demodulation module is weak, and some noise signals are also added to the demodulated signal, so that the demodulated signal needs to be amplified first to obtain the amplified demodulated signal with a strong signal; then, the amplified demodulation signal is subjected to active filtering processing to output a spectrally pure demodulation signal. This helps to further improve the purity of the demodulated signal, and thus improves the demodulation accuracy of the doppler signal.
According to another aspect of the present invention, the present invention provides a doppler signal demodulation system. Specifically, as shown in fig. 6, the doppler signal demodulation system 10 includes a pre-amplification module 11, a band-pass filtering module 12, and a phase-locked loop demodulation module 13. The pre-stage amplification module 11 is configured to amplify the acquired doppler signal to obtain an amplified doppler signal, where the doppler signal is a detected doppler frequency shift caused by a motion of an object to be measured; the band-pass filtering module 12 is configured to perform band-pass filtering processing on the amplified doppler signal to obtain a filtered doppler signal as an input signal, so that additional noise in the input signal is eliminated; the phase-locked loop demodulation module 13 is configured to perform phase-locked demodulation on the input signal to output a demodulated signal, where a voltage of the demodulated signal is proportional to a frequency of the doppler signal, so as to calculate a moving speed of the object to be measured through the demodulated signal.
More specifically, as shown in fig. 6, the pll demodulation module 13 includes a phase comparator 131, a loop filter 132, and a voltage-controlled oscillator 133, which are communicably connected to each other, wherein the phase comparator 131 is configured to compare a phase difference between the input signal and a comparison signal output by the voltage-controlled oscillator 133 to obtain an error voltage; the loop filter 132 is configured to filter a modulated carrier component in the error voltage to obtain a control voltage; the voltage-controlled oscillator 133 is configured to output the comparison signal with a corresponding frequency based on the control voltage, so that the comparison signal and the input signal have a predetermined frequency relationship; and the loop filter 132 is further configured to output the control voltage as the demodulation signal.
Of course, in this embodiment of the present invention, as shown in fig. 6, the doppler signal demodulation system 10 may further include a post-amplification module 14 and an active filtering module 15. The post-amplification module 14 is configured to amplify the demodulated signal to obtain an amplified demodulated signal; the active filtering module 15 is configured to perform active filtering processing on the amplified demodulated signal to filter noise in the amplified demodulated signal, so as to output a demodulated signal with a pure frequency spectrum.
Illustratively, the doppler signal demodulation system 10 can be implemented as, but is not limited to, a doppler signal demodulation circuit, wherein the pre-amplification module 11 can be implemented as two amplifiers arranged in series, the band-pass filtering module 12 can be implemented as a band-pass filter, the phase-locked loop demodulation module 13 can be implemented as a CD4046 phase-locked loop circuit, the post-amplification module 14 can be implemented as an amplifier, and the active filtering module 15 can be implemented as an active filter.
In this way, when a photoelectric detector FM signal (i.e., a doppler signal) is amplified to a certain degree by the amplifier, the weak signal is filtered by the band-pass filter BHP and then is input to the 14 pins of the CD4046 phase-locked loop circuit as an input signal; then, the phase-locked demodulation processing is carried out through the CD4046 phase-locked loop circuit, and an analog signal (namely control voltage) is output from a pin 10 of the CD4046 phase-locked loop circuit to serve as a demodulation signal; and finally, amplifying the weak demodulation signal through the amplifier, and filtering through the active filter to output the demodulation signal with pure frequency spectrum. For example, a frequency modulation signal FM (carrier signal: fc ═ 38kHz sine wave; Ucm ═ 2.5V; modulation signal: F ═ 1kHz, U Ω m ═ 1V sine wave) is input; the Doppler velocity measurement corresponding to the demodulation signal output by the Doppler signal demodulation system is 10mm/s, and the demodulation effect is very good.
It should be noted that, since the operating frequency of the pll demodulation module (e.g., CD4046 pll circuit) is usually a narrow range, and the pll demodulation module cannot operate normally once the center frequency of the input signal is not within the range of the operating frequency. Therefore, in the above embodiment of the present invention, the doppler signal demodulation system 10 can only be ensured to work normally by ensuring that the frequency of the doppler signal obtained by the laser vibration (velocity) measuring instrument matches the operating frequency of the phase-locked loop demodulation module.
However, in order to reduce the frequency modulation receiving threshold of the doppler signal demodulation system, expand the application range, and facilitate normal demodulation of doppler signals with different frequencies, another embodiment of the present invention provides a doppler signal demodulation method and a system thereof. Specifically, as shown in fig. 7, the doppler signal demodulation method includes the steps of:
s210: amplifying the obtained Doppler signals to obtain amplified Doppler signals, wherein the Doppler signals are detected Doppler frequency shifts caused by the movement of the measured object;
s220: performing frequency mixing processing on the amplified Doppler signals to obtain Doppler signals after frequency mixing, wherein the center frequency of the Doppler signals after frequency mixing is matched with the working frequency of a phase-locked loop demodulation module;
s230: performing band-pass filtering processing on the mixed Doppler signals to obtain filtered Doppler signals as input signals, so that additional noise in the input signals is eliminated;
s250: performing phase-locked demodulation on the input signal by the phase-locked loop demodulation module to output a demodulated signal;
s260: amplifying the demodulation signal to obtain an amplified demodulation signal; and
s270: and performing active filtering processing on the amplified output signal to filter noise in the amplified demodulated signal so as to obtain a demodulated signal with a pure frequency spectrum, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated through the demodulated signal.
It should be noted that, because the center frequency of the doppler signal after the frequency mixing is matched with the operating frequency of the pll demodulation module (for example, the center frequency of the doppler signal after the frequency mixing is equal to the center value of the operating frequency), the center frequency of the input signal obtained by filtering the doppler signal after the frequency mixing is also matched with the operating frequency of the pll demodulation module, so that no matter whether the center frequency of the obtained doppler signal is greater or smaller, the center frequency of the input signal can be ensured to be matched with the operating frequency of the pll demodulation module, so as to ensure the normal operation of the pll demodulation module, thereby expanding the application range of the doppler signal demodulation method.
It should be noted that if the amplitude of the input signal is relatively large, even if the center frequency of the input signal is still within the working frequency range of the pll demodulation module (i.e., the center frequency of the input signal matches the working frequency of the pll demodulation module), the demodulation accuracy of the pll demodulation module is severely reduced due to the fact that the peak value of the input signal exceeds the working amplitude range of the pll demodulation module, and even the pll demodulation module cannot normally work. Therefore, in this embodiment of the present invention, as shown in fig. 7, between the step S230 and the step 250, the doppler signal demodulation method may further include the steps of:
s240: and carrying out amplitude limiting processing on the input signal so as to control the amplitude pulsation of the input signal, so that the amplitude of the input signal is matched with the working amplitude of the phase-locked loop demodulation module.
Therefore, the Doppler signal demodulation method not only can accurately demodulate the Doppler signal with smaller amplitude, but also can accurately demodulate the Doppler signal with larger amplitude, thereby further expanding the application range of the Doppler signal demodulation method.
According to another aspect of the present invention, this embodiment of the present invention further provides a doppler signal demodulation system 20. Specifically, as shown in fig. 8, the doppler signal demodulation system 20 includes a pre-amplification module 21, a mixing module 22, a band-pass filtering module 23, and a phase-locked loop demodulation module 25. The pre-stage amplification module 21 is configured to amplify the acquired doppler signal to obtain an amplified doppler signal, where the doppler signal is a doppler frequency shift obtained by detecting a movement velocity of an object to be measured; the frequency mixing module 22 is configured to perform frequency mixing processing on the amplified doppler signal to obtain a frequency-mixed doppler signal, where a center frequency of the frequency-mixed doppler signal is matched with a working frequency of a phase-locked loop demodulation module; the band-pass filtering module 23 is configured to perform band-pass filtering processing on the mixed doppler signal to obtain a filtered doppler signal as an input signal, so that additional noise in the input signal is eliminated; the phase-locked loop demodulation module 25 is configured to perform phase-locked demodulation on the input signal to output a demodulated signal, where a voltage of the demodulated signal is proportional to the doppler shift, so as to calculate a moving speed of the object to be measured through the demodulated signal.
It is noted that in an example of the present invention, the mixing module 22 of the doppler signal demodulating system 20 can be, but is not limited to being, implemented as a mixer for adding the amplified doppler signal to a base signal, thereby changing the frequency spectrum of the amplified doppler signal so that the center frequency of the mixed doppler signal matches the operating frequency of the phase-locked loop demodulating module. It will be appreciated that the mixer may be an adding mixer or a subtracting mixer.
Further, in an example of the present invention, as shown in fig. 8, the phase-locked loop demodulation module 25 includes a phase comparator 251, a loop filter 252, and a voltage-controlled oscillator 253 communicably connected to each other, wherein the phase comparator 251 is configured to compare a phase difference between the input signal and a comparison signal output by the voltage-controlled oscillator 253 to obtain an error voltage; the loop filter 252 is configured to filter a modulated carrier component in the error voltage to obtain a control voltage; the voltage-controlled oscillator 253 is configured to output the comparison signal with a corresponding frequency based on the control voltage, so that the comparison signal and the input signal have a predetermined frequency relationship; and the loop filter 252 is further configured to output the control voltage as the demodulation signal.
Of course, in this embodiment of the present invention, as shown in fig. 8, the doppler signal demodulation system 20 may further include a post-amplification module 26 and an active filtering module 27. The post-amplification module 26 is configured to amplify the demodulated signal to obtain an amplified demodulated signal; the active filtering module 27 is configured to perform active filtering processing on the amplified demodulated signal to filter noise in the amplified demodulated signal, so as to output a spectrally pure demodulated signal.
It should be noted that, as shown in fig. 8, the doppler signal demodulation system 20 may further include a limiting module 24, configured to perform a limiting process on the input signal to control the amplitude ripple of the input signal, so that the amplitude of the input signal matches the working amplitude of the phase-locked loop demodulation module.
The previous description is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
It will be appreciated by persons skilled in the art that the embodiments of the invention described above and shown in the drawings are given by way of example only and are not limiting of the invention. The objects of the invention have been fully and effectively accomplished. The functional and structural principles of the present invention have been shown and described in the examples, and any variations or modifications of the embodiments of the present invention may be made without departing from the principles.
Claims (16)
1. A method for demodulating a doppler signal, comprising the steps of:
amplifying the obtained Doppler signals to obtain amplified Doppler signals, wherein the Doppler signals are detected Doppler frequency shifts caused by the movement of the measured object;
performing band-pass filtering processing on the amplified Doppler signal to obtain a filtered Doppler signal as an input signal, wherein the filtered Doppler signal is used for filtering additional noise in the input signal; and
and performing phase-locked demodulation on the input signal by using a phase-locked loop demodulation module to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated by the demodulated signal.
2. The doppler signal demodulation method according to claim 1, wherein the step of phase-locked demodulating the input signal by the phase-locked loop demodulation module to output a velocity demodulation signal as an output signal comprises the steps of:
comparing, by a phase comparator of the pll demodulation module, a phase difference between the input signal and a comparison signal output by a voltage controlled oscillator of the pll demodulation module to obtain an error voltage;
filtering a modulation carrier component in the error voltage by a loop filter of the phase-locked loop demodulation module to obtain a control voltage;
outputting a comparison signal of a corresponding frequency through the voltage-controlled oscillator based on the control voltage, so that the comparison signal and the input signal have a predetermined frequency relation; and
and outputting the control voltage as the demodulation signal.
3. The doppler signal demodulation method according to claim 2, wherein a frequency of the comparison signal is equal to a frequency of the input signal.
4. The doppler signal demodulation method according to claim 2, wherein a ratio between the frequency of the comparison signal and the frequency of the input signal is kept constant.
5. The doppler signal demodulation method according to claim 2, wherein a difference between the frequency of the comparison signal and the frequency of the input signal is kept constant.
6. The doppler signal demodulation method according to any one of claims 1 to 5, further comprising, between the amplification processing step and the filtering processing step, the steps of:
and performing frequency mixing processing on the amplified Doppler signals to obtain frequency-mixed Doppler signals, wherein the center frequency of the frequency-mixed Doppler signals is matched with the working frequency of the phase-locked loop demodulation module.
7. The doppler signal demodulation method according to claim 6, further comprising, between said filtering processing step and said phase-locked demodulation step, the steps of:
and carrying out amplitude limiting processing on the input signal so as to enable the amplitude of the input signal to be matched with the working amplitude of the phase-locked loop demodulation module.
8. The doppler signal demodulation method of claim 7, further comprising, after the phase-locked demodulation step, the steps of:
amplifying the demodulation signal to obtain an amplified demodulation signal; and
and performing active filtering processing on the amplified demodulation signal to filter noise in the amplified demodulation signal.
9. A doppler signal demodulation system, comprising:
the pre-stage amplification module is used for amplifying the obtained Doppler signal to obtain an amplified Doppler signal, wherein the Doppler signal is a detected Doppler frequency shift caused by the movement of a measured object;
a band-pass filtering module, configured to perform band-pass filtering processing on the amplified doppler signal to obtain a filtered doppler signal as an input signal, so as to filter additional noise in the input signal; and
and the phase-locked loop demodulation module is used for performing phase-locked demodulation on the input signal to output a demodulated signal, wherein the voltage of the demodulated signal is in direct proportion to the Doppler frequency shift, so that the movement speed of the measured object is calculated through the demodulated signal.
10. The doppler signal demodulation system of claim 9, wherein the phase-locked loop demodulation module comprises a phase comparator, a loop filter, and a voltage-controlled oscillator communicably connected to each other, wherein the phase comparator is configured to compare a phase difference between the input signal and a comparison signal output through the voltage-controlled oscillator to obtain an error voltage; the loop filter is used for filtering a modulation carrier component in the error voltage to obtain a control voltage; the voltage-controlled oscillator is used for outputting a comparison signal with a corresponding frequency based on the control voltage so that the comparison signal and the input signal have a preset frequency relation; and the loop filter is further configured to output the control voltage as the demodulation signal.
11. The doppler signal demodulation system of claim 10, further comprising a mixing module for mixing the amplified doppler signal to obtain a mixed doppler signal, wherein a center frequency of the mixed doppler signal matches an operating frequency of the phase locked loop demodulation module.
12. The doppler signal demodulation system of claim 11, further comprising a clipping module for clipping the input signal to match the amplitude of the input signal to the operating amplitude of the phase locked loop demodulation module.
13. The doppler signal demodulation system of claim 12, further comprising a post-amplification module and an active filtering module, wherein the post-amplification module is configured to amplify the demodulated signal to obtain an amplified demodulated signal; the active filtering module is used for performing active filtering processing on the amplified demodulation signal so as to filter noise in the amplified demodulation signal.
14. The doppler signal demodulation system of any one of claims 9 to 13, wherein the phase-locked loop demodulation module is a phase-locked loop demodulation circuit.
15. The doppler signal demodulation system of claim 14, wherein the pre-amplification module is a wideband pre-op amp circuit.
16. The doppler signal demodulation system of claim 15, wherein the band pass filtering module is a band pass filter or an intermediate frequency filter.
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